Phenol plant effluent treatment

ABSTRACT

A PROCESS FOR IMPROVING THE BIODEGRADABILITY OF A PHENOL PLANT EFFLUENT STREAM BY DECOMPOSING OR CHEMICALLY MODIFYING CERTAIN BIOCIDES CONTAINED THEREIN.

United States Patent US. Cl. 210-48 1 5 Claims ABSTRACT OF THE DISCLOSURE A process for improving the biodegradability of a phenol plant efiluent stream by decomposing or chemically modifying certain biocides contained therein.

The present invention relates to a process for the biodegradation of a phenol plant aqueous efiluent stream.

For the purpose of this invention phenol plant is defined as a plant in which phenol is produced by the oxidation of cumene followed by decomposition of the oxidation product, cumene hydroperoxide, to phenol and acetone.

Effluent streams from phenol plants normally contain water, traces of phenol and acetone and other impurities. Such eflluent streams give very low results when tested for biological oxygen demand (BOD) despite their high chemical oxygen demand (COD). It is believed that this is due to the presence of certain biocides, other than phenol itself which sten'lise the microorganism responsible for biodegradation in, for example, the standard BOD determination. It is very desirable that the effluent stream from a phenol plant should be biodegradable.

An improved biodegradation process has now been discovered in which certain biocides present in the efiluent stream are removed prior to biodegradation.

Thus according to the present invention there is provided a process for the biodegration of a phenol plant efiluent stream which process comprises treating the phenol plant eflluent stream with sulphur dioxide or a sulphur-containing compound prior to contacting the effluent with an activated sludge biodegration unit.

Suitable sulphur-containing compounds include soluble metal sulphites, bisulphites and metal sulphides. The preferred compounds are sodium sulphite, sodium bisulphite and sodium sulphide.

Treatment of the efliuent with sulphur dioxide necessitates the addition of further alkali to neutralise the free acid remaining after partial neutralisation by sodium carbonate contained in the eflduent stream. Removal of biocides from the eflluent stream by treatment with sulphur-containing Compounds such as sodium sulphite, sodiuum bisulphite or sodium sulphide is thus preferred because further addition of alkali is avoided. A convenient source of caustic sulphided liquor is the eifiuent stream from an ethylene cracking unit. A suitable source of sodium bisulphite liquor may be, for example, paper mill waste streams.

It is believed that the treatment with sulphur dioxide or the sulphur-containing compound decomposes or chemically modifies the biocides present in the eflluent stream, thereby facilitating its biodegradation.

The invention is illustrated by the following example:

EXAMPLE The chemical oxygen demand (COD) and the biological oxygen demand (BOD) of a sample of a phenol plant efiluent were measured before and after treatment of the etlluent with 0.4% of sulphur dioxide, a quantity such that no excess sulphite ion could be detected after treatment. The results were as follows:

Following the treatment with sulphur dioxide the effiuent stream was contacted with activated sludge, slurried and allowed to settle.

The example shows that treatment with sulphur dioxide greatly increased the test result for BOD, that is to say the biodegradability of the effluent stream.

We claim:

1. A process for the treatment of a phenol plant effluent stream to facilitate biodegradation thereof which comprises treating the phenol plant efiluent stream containing water, phenol, acetone and other impurities with sulphur dioxide, or a soluble metal sulphite, bisulphite, or sulphide.

2. A process as claimed in claim 1 wherein the compound is selected from sodium sulphite, sodium bisulphite and sodium sulphide.

3. A process as claimed in claim 1 wherein the phenol plant efiluent stream is treated with the sulphided eflluent stream from an ethylene cracking unit.

4. A process as claimed in claim 1 wherein the phenol plant effluent stream is treated with a paper mill waste stream.

5. A process for the biodegradation of a phenol plant efiluent stream which comprises treating the phenol plant efliuent stream containing water, phenol, acetone and other impurities, with sulphur dioxide, or a soluble metal sulphite, bisulphite, or sulphide, and then contacting said efiiuent with an activated sludge biodegradation unit.

References Cited UNITED STATES PATENTS 3/1959 Story 21050 X 10/1966 Millar 2l0--15 X OTHER REFERENCES MICHAEL ROGERS, Primary Examiner US. Cl. X.R. 210-59 

